1. Field of the Invention
The present invention relates to an injection molding machine and, more particularly, to a plastic injection molding machine.
2. Description of the Related Art
A conventional injection molding machine in accordance with the prior art shown in FIG. 1 comprises a power device and a die assembly connected with the power device. The power device includes a movable plate having a first screw hole and a second screw hole, a primary motorized cylinder 71 having a primary threaded shaft screwed through the first screw hole of the movable plate, and a secondary motorized cylinder 72 having a secondary threaded shaft screwed through the second screw hole of the movable plate. In operation, the primary motorized cylinder 71 and the secondary motorized cylinder 72 are driven by a driver to rotate the primary threaded shaft and the secondary threaded shaft. In such a manner, the movable plate is moved by rotation of the primary threaded shaft of the primary motorized cylinder 71 and the secondary threaded shaft of the secondary motorized cylinder 72 to drive the die assembly so as to close or open the die assembly. The conventional injection molding machine further comprises a processor to calculate some factors. The factors include a ratio of the position, torque and speed of the primary threaded shaft of the primary motorized cylinder 71 and the secondary threaded shaft of the secondary motorized cylinder 72. Thus, the processor calculates the factors to control the torque output of the primary threaded shaft of the primary motorized cylinder 71 and the secondary threaded shaft of the secondary motorized cylinder 72. However, each of the factors of the primary motorized cylinder 71 and the secondary motorized cylinder 72 exists a tolerance so that the total tolerance of all of the factors will produce a greater differential between the torque output values of the primary motorized cylinder 71 and the secondary motorized cylinder 72. Thus, the primary threaded shaft of the primary motorized cylinder and the secondary threaded shaft of the secondary motorized cylinder are easily deflected due to the differential between the torque output values of the primary motorized cylinder and the secondary motorized cylinder, thereby affecting operation of the injection molding machine. As shown in FIG. 1, a graph of the torque of the primary motorized cylinder 71 and the secondary motorized cylinder 72 is drafted, wherein the horizontal coordinate indicates the time, and the vertical coordinate indicates the distance of displacement. The unit of the time is millisecond (ms), and the unit of the distance of displacement is nanometer (Nm). It is clear that the normal torque output values of the primary motorized cylinder 71 and the secondary motorized cylinder 72 have a greater differential.